1. Field of the Invention
The invention relates to a medical monitoring device. More particularly, the invention relates to a device for monitoring the condition and location of a subject or patient.
2. Description of the Prior Art
Modern medical practice makes extensive use of electronic vital signs monitoring. As technology has progressed, electronic monitoring devices have become more compact, easier to use, and have been made available to larger segments of the patient population. Today, most electronic monitors are what are termed “bedside monitors.”
A bedside monitor consists of an electronics and display unit placed in close proximity to a patient bed. Cables connect the monitor to various sensors attached to the patient. While such arrangements have become highly developed, and permit comprehensive monitoring of the patient, the disadvantages are obvious. A patient can only be monitored when confined to bed, or otherwise restricted to the immediate vicinity of the monitor, as dictated by the connecting cables.
Portable or transportable monitors have been developed to allow the patient to be moved within the hospital, or even between healthcare facilities. Such monitors are quite similar to traditional bedside monitors, but are made somewhat smaller and lighter in weight, and have provision to operate for some time from internal battery power. But such devices remain sufficiently heavy and bulky that they require special attention to move along with the patient. Often, the monitor is provided with a bracket or other arrangement allowing it to be attached to the wheeled bed occupied by the patient during transport. While such an arrangement makes it possible to relocate a patient while continuing monitoring, it does not permit normal ambulation of the patient.
In many cases, patients are sufficiently able-bodied that they may ambulate normally, and are not confined to bed, yet it is desired to continuously monitor their condition. Indeed, in some cases ambulation of the patient is a necessary part of medical care, as in the case of a heart patient where the exertion associated with walking and other normal activity may be necessary to reveal an underlying heart condition. To serve these cases, patient-worn monitoring devices have been developed. Often, such devices are limited to monitoring a single vital sign. As the heart may be considered the most vital organ, the usual parameter to be monitored is the electrocardiogram, or ECG.
Patient-wearable devices used to monitor a patient's ECG take two general forms. One form of device, often known as a holter monitor, simply records the patient's ECG signal for later analysis. The particular advantage of this sort of device is that monitoring can take place at any location, while the patient is going about normal daily activities. However, an obvious disadvantage is that there is no immediate indication of a deterioration in the patient's condition. Therefore, an alternate device, known as a telemetry monitor, has been developed. Such a device acquires the patient's ECG signal, and transmits it by radio link to a central monitoring and display location, where the ECG signal can be observed by clinical personnel and automated analysis systems. Any change in the patient's condition requiring clinical intervention is therefore immediately apparent and medical assistance can be dispatched to the patient. The disadvantage of telemetry systems is that they are operable only within premises where suitable receiving equipment is provided.
Current ambulatory ECG monitors found in clinical applications use electrodes of a type and configuration based on bedside monitor practice. Generally, three to five adhesive electrodes are attached to the body in locations disposed on the chest. These electrodes are connected by leadwires or a cable to the monitor electronics. The monitor electronics is arranged in a wearable housing, generally supported by means of a pouch, sling, or belt clip. This arrangement is somewhat inconvenient, due to the presence of the leadwires and the bulk, weight, and method of support of the monitor electronics. Further, some skill is necessary to properly attach the electrodes, connect the leadwires and set the monitor in action. As such, monitoring devices of this type are only used in such clinical cases where the inconvenience and cost of the skilled application are justified.
Electrocardiogram devices using conventional electrode configurations can yield considerable information about the condition of the heart by skilled interpretation of the ECG waveforms produced. However, in many cases, even in clinical practice, such interpretation is not performed, and the monitor is used only to measure the patient's heart rate. This is always the case in certain non-clinical ECG applications, such as when the ECG signal is used to determine the pulse rate during exercise. In this case, conventional placement of electrodes can be abandoned in favor of electrode configurations which facilitate convenient application of the monitoring device. Exercise ECG monitors are often configured as a small electronics housing secured by a belt tightened around the wearer's chest. The housing contains a pair of electrodes which contact the chest and acquire an ECG signal. The electronics trigger on each heartbeat and transmit a signal to a nearby readout device. The readout device counts the trigger signals within a unit time and displays the pulse rate.
While such exercise monitors are far simpler to apply and lack the objectionable leadwires and separate electronics box of clinical ambulatory monitors, they do not answer fully to clinical purposes, even where it is only desired to measure the heart rate. The electronics, signal processing and signal transmission used by these devices are not well adapted to clinical requirements. These defects, however, can be remedied by modification of the electronics in well-known ways. Of greater importance is the fact that the encircling belt is not well adapted to long term wear. In order to secure the device against accidental displacement, the belt must be tightened to a degree that proves objectionable over an extended period. If the belt is loosened one runs the risk of a temporary loss of electrode contact during exercise or while the patient is laying or shifting in bed. Further, the electrodes used in commercial exercise monitors often depend on some degree of perspiration to reduce the electrical resistance of the electrode contact. While perspiration is inevitably present in exercise sufficiently strenuous to merit pulse rate monitoring, its presence cannot be assumed in the clinical setting. Finally, even if tension and electrode issues were resolved, the position of the device across the chest is not optimal for patient and clinician convenience. Application of the device to this region can in some cases constitute an insult to patient dignity. More importantly, the position of the belt may interfere with the application of defibrillator electrodes, the placement of a stethoscope, or other common medical procedures.
It is desirable to expand clinical electronic monitoring to a greater population of patients. This is only practical if an arrangement less unwieldy than traditional clinical ambulatory monitors is adopted. While commercial exercise monitors considerably simplify the monitoring arrangement, they still do not answer well to the needs of such expanded clinical monitoring.
Patient-worn devices also exist which give an indication of the location of the patient. A typical prior art system is described in U.S. Pat. No. 4,958,645 entitled Multi-Channel Digital Medical Telemetry System, which issued on Sep. 25, 1990 to Cadell et al. The medical radio telemetry system described therein utilizes a plurality of antennas which are distributed throughout a hospital or other premises. The patient is outfitted with a radio receiver and transmitter to collect a patient physiological signal, including, for example, the patient's temperature, heart rate, pacer rate, respiration rate, brain activity level, and blood pressure level. The transmitter and receiver associated with the patient operate in conjunction with one or more room locator transmitters spaced in rooms where the patient is being monitored. The room locator transmitters emit signals indicative of the room they are emanating from. Signals from the room locator transmitters are combined with the patient signals so as to enable hospital staff to monitor the location of the patient.
U.S. Pat. No. 4,981,141, entitled Wireless Electrocardiographic Monitoring System, issued on Jan. 1, 1991 to Segalowitz, discloses an electrocardiographic monitoring system where the patient's heart-signaling sensing electrodes are each coupled to the heart-signal monitor/recorder by wireless transmitters and corresponding wireless receivers in a base unit. Each transmitter/receiver combination operates at a separate radio frequency to provide a zero or reference signal at the base unit which is used to modulate a signal transmitter at the base unit. Each modulated signal, when received and demodulated, provides information concerning signals sensed by an electrode carried by the patient, such as, for example, the right-leg electrode, etc.
It is clear from the above that it is extremely desirable to monitor various vital signs of an ambulatory patient. This is even more important due to the recent trend to get patients ambulating as soon as possible. It is also important to determine the location of a monitored patient within, for example, the confines of a hospital or other area so as to ensure expedient care, such as in the case of an emergency.
Despite the devices that are currently available for monitoring ambulatory patients, there is a need for improved devices that are light in weight, lower in cost and easy to use.